This invention relates to drill bits, and more particularly to rotary drill bits with diamond cutting elements used in the drilling of bore holes in earth formations.
Earth boring diamond drill bits may typically include an integral bit body which may be of steel faced with an abrasion-resistant material such as tungsten carbide or may itself be fabricated of a hard metal matrix material such as tungsten carbide. A plurality of diamond cutting elements are mounted along the exterior face of the bit body. Each diamond cutter typically may be mounted on a stud the other end of which is mounted in a recess in the exterior face of the bit body, or the cutter mount may be integrally cast with the matrix of the bit body.
The cutting elements are positioned along the leading edges of the bit body so that as the bit body is rotated in its intended direction of use, the cutting elements engage and drill the earth formation. In use, tremendous forces are exerted on the cutting elements, particularly against the face thereof in the forward to rear direction as the bit is rotated. Additionally, the bit and cutting elements are subjected to substantial abrasive forces. In some instances, impact, lateral, and/or abrasive forces have caused drill bit failure and cutter loss.
A significant problem encountered when drilling in certain earth formations such as shales, clay, and other water reactive, sticky formations known as "gumbo" has been the tendency of such bits to become clogged during operation. In dealing with such earth formations, bits have been designed with relatively large cutters with strong hydraulics in the proximity of the cutters to remove the cuttings from the cutter faces with a high volume, high velocity, hydraulic fluid flow.
As synthetic diamond technology has advanced, it is now possible to provide large diamond disc cutters up to two inches in diameter for use on bits. These very large cutters have been helpful in drilling in "gumbo" formations. However, the large diameter of the cutting elements has caused problems in providing secure attachment thereof to the exterior face of the rotary drill bits. To accommodate such large diameter cutters, drill bits have been fabricated with outwardly extending shoulders or protrusions on which the cutters may be mounted. However, this leaves a relatively small structure beneath and behind the cutter faces to support the cutters. Additionally, blades, ridges and other structures having multiple cutters mounted thereon and extending significant distances from the main profile of the bit body are also becoming more common, presenting similar problems.
While tungsten carbide or other hard metal matrix bits are highly erosion resistant, such materials are relatively brittle and can crack upon being subjected to the impact forces encountered during drilling. Typically, such cracks have occurred proximate where the cutting element support structures join the matrix body. The shoulders or protrusions on the exterior of the drill bits to accommodate large diameter cutting exposes these areas of the bit to high impact and shear forces. Bits having large cutter elements thereon extending outwardly from the body of the bit are particularly susceptible to cracking and failure due to these high impact and shear forces. If the cutting elements are sheared from the drill bit body, the expensive diamonds on the cutter elements are lost, and the bit may cease to drill.
Accordingly, there is a need in the art for a drill bit having increased impact strength and resistance to cracking, particularly in areas supporting the cutter elements.